Possible German great coat

Article about: I have picked up a grey great coat from an army surplus shop but have lost a button. Perhaps identification of the coat will help me find a suitable replacement button/ button set. It is gre

Possible German great coat

I have picked up a grey great coat from an army surplus shop but have lost a button. Perhaps identification of the coat will help me find a suitable replacement button/ button set.
It is grey, double-breasted with round, flat, silver-coloured buttons with many inverted dimples (the best way I can think of describing them).
There are six buttons over-all on the front with an extra one under the right-hand lapel for particular cold. The lining is creased and a a similar colour to the wool of the coat.
Perhaps you can suggest the origin and a place to get a replacement button or two, or possibly a suitable set of replacement buttons.